Constant voltage positive bias supply



Nov. 13, 1951 HOBBS ETAL 2,575,107

CONSTANT VOLTAGE POSITIVE BIAS SUPPLY Filed April 50, 1946 Patented Nov. 13,1951

CONSTANT VOLTAGE POSITIVE BIAS SUPPLY Charles F. Hobbs, Watertown, and Norman B. Saunders, Cambridge, Mass, assignors to the United States of America as represented by the Executive Secretary of the Ofifice of Scientific Research and. Development Application April 30, 1946, Serial No. 666,027

cilloscope. One suggestion has been to attempt to supply controlled bias to the tubes in the first pulse amplifier stage by means of a voltage divider circuit. However, due to the peculiar connection of the potentiometers in this type of cirouit, changing any one potentiometer changes 1 the resistance of the circuit and hence the bias voltage to all amplifiers. This interrelation is unsatisfactory.

An object of the invention therefore is to overcome the difficulty noted and to devise a circuit capable of producing proper bias without undesirable inter-action between potentiometers.

We have found that one suitable means of attaining this objective consists in the combination with a voltage divider of a circuit of a cathode follower type which includes a glow discharge type regulator adapted to be attached to the cathode follower so that its bias is automatically changed by changes in the cathode voltage.

The figure in the accompanying drawing is a schematic diagram of the circuit of the invention.

A source of potential, not shown, having an intermediate point grounded, has its positive terminal connected to wire It and its negative terminal connected to wire H. A voltage divider represented by resistances R1 and R2 is bridged across wires ill and H. The slider i2 is connected to ground through a, second voltage divider having resistances R3 and R4. The slider it on resistances R3 and R4 is connected to grid it: of the A element of double triode V1. The plate potential for this tube is supplied between wire iii and ground and is indicated by E1. The negative potential applied between terminal H and ground provides bias potential and excitation for voltage regulator tube V3.

The load whose voltage is to be regulated is represented schematically by theresistance Re, which, as an example, may have a value varying from 500 to 5000 ohms. This load resistance is connected between the cathodes 19 of double triode V4 and ground. The potential to be regulated is indicated at E2.

A voltage divider, represented by resistances R5 and R11, is connectedfrom cathode IQ of tube 5 Claims. (01. 323-22) V4 to the source of negative potential H. The slider 29 on resistance R5 is connected to grid 22 of element B of double triode V1. Anodes i4 and 2| are connected together and supplied through a common anode resistor R7. Anodes l4 and 2: are connected to grid "25 of triode V2. Cathode 23 is connected to ground through cathode resistor Rs.

Tube V2 is a, cathode follower, well known in the art. Its anode 24 is connected directly to the-source of positive potential It while its cathode 26 has a cathode resistor R9 connected indirectly to ground through cathode resistor R5 of tube V113. This connection provides a regenerative feed back, which adds to the sensitivity and is an important feature of the invention.

The output of the cathode follower V2 may be applied to the grid of the load current tube V4 by connecting the cathode 26 directly to grids it of V4, connected in parallel. In the preferred arrangement, a voltage regulator tube V3, of the glow discharge type, is interposed, the cathode of V2 being connected to the anode 28 of the glow discharge tube V3 while cathode 29 is connected to grids l8. A high resistance R10 is connected from cathode 29 of V3 to the source of negative potential I I. This provides the normal excitation required for the operation of the glow discharge tube. A high resistance R8 is connected from wire Hi to cathode 23 of VlB to provide the desired positive bias.

The circuit operates in the following manner:

Any change in output voltage E2 causes a corresponding change in the potential of grid 22 of tube V13. The change in grid voltage may be slightly smaller than the change in E2 (for setting of R5 toward the R11 end) but will always be proportional thereto. The change in grid voltage on VH3 is amplified and applied to the grids iii of the output tubes V4 in the opposite phase to the original change in E2. The reversal of phase is accomplished by connecting anode iii of VlB directly togrid 25 of tube V2. This effect is then transmitted to V4 without further reversal of phaseby cathode follower action of V2, from cathode 26 through gas tube V3 to grids l8. Gas tube V3 is a constant voltage device.

The amplified reversed phase voltage applied to the control grids [8 of the output tube V4 opposes the voltage change on the cathode load resistance RL by cathode follower action of V2. A portion of the cathode voltage of V2 is applied to the cathode of VlB as a regenerative voltage to increase the gain of that stage. The amount of regenerative feedback should be adjusted to the critical amount required to cause the stage to be unstable with the negative feedback path disconnected at X.

The purpose of tube Vm is to provide compensation for fluctuations in supply voltage. This is accomplished by applying a fraction of the supply voltage derived from voltage divider R3, R4 to control grid [5 of VlA- Anodes l4 and 2| have a common anode resistor R7; consequently the output voltages of both tubes, VIA andVna, are combined and applied to grid 25 of cathode follower V2 and thence to grids l8 of output tube V4. It will be seen that a reduction in supply voltage E1 causes a reduction in grid voltage of VIA, an increase in the plate potential of VIA, an

increase in grid voltage of V2, an increase in grid voltage of V4, an increase in load current through R1,, and consequently a compensation for the initial drop in supply voltage E1.

If the adjustment of R5 is changed the voltage between the output and the grid of VlB is changed. This results in a change in the operating point of that tube with a corresponding change in the output voltage from V4. For example; suppose the grid of V113 is made more negative by moving the slider of R5 toward the negative end. This results in a decreased flow of plate current through V13 with a resultant increase in its plate voltage. This increased plate voltage increases the grid voltage on V4 and consequently increases the output voltage appearing across the load resistance R1. since V4 is a cathode follower.

This circuit may be applied to test equipment where a very constant low voltage supply capable of delivering any desired amount of current is needed. The load current may be increased indefinitely by increasing the number of triodes in parallel in the final cathode follower stage V4.

While we have shown a preferred embodiment of our invention, it should be understood that various changes and modifications may be resorted to, in keeping with the spirit of the invention as defined by the appended claims.

We claim:

1. A system for regulating voltage comprising, a, source of direct current potential supp having an intermediate point grounded, a first tube, a second tube and an output tube each having at least an anode, cathode and control grid, an output circuit connected from the output tube cathode to said ground, a voltage divider connected from the cathode of said output tube to the negative source of supply, a connection from the voltage divider to the first grid, a connection from the first tube anode to the second tube grid, negative bias means for the output tube including a gas discharge tube connecting the cathode of the second tube to the grid of the output tube and a resistor connecting said output grid to the negative source of supply, an anode resistor for the first tube, and a regenerative feed back connection including a cathode resistor for the first tube connected to said ground and a cathode resistor for the second tube connected to the first cathode.

2. A system for regulating voltage comprising a source of direct current potential supply having an intermediate point grounded, a first tube, a second tube and an output tube each having at least an anode, cathode and grid, an output circuit connected from the cathode of the output tube to said ground, a voltage divider connected from the cathode of said output tube to the negative source of supply, a connection from the volt-.

age divider to the first grid, a direct connection from the first tube anode to the second tube grid, a gas discharge tube connecting the cathode of the second tube to the grid of the output tube and a resistor connected from said output grid to the negative source of supply, an anode and a cathode resistor for the first tube, and a regenerative feed back connection including a cathode resistor for the second tube connected to the first tube cathode.

3. A system for regulating voltage comprising a source of direct current potential supply having an intermediate point grounded, a load impedance and a load current vacuum tube having at least an anode, cathode and grid, connected in series from the positive source to ground, and

vacuum tube means responsive to the potential variations across the load resistance for controlling the grid of the load current tube, said vaccum tube means including a first tube having an anode and cathode and an anode and cathode resistor respectively in series bridged from ground to the positive source'of potential supply, a cathode follower tube having its cathode resistor connected to the cathode of the first tube, a potential divider bridged from the cathode of said load tube to the negative source of supply, and a connection from the voltage divider to the grid of the first tube, and negative bias means interposed between the second tube and the output tube including a gas discharge tube connecting the second tube cathode to the grid of the output tube and a resistor connected from the output tube grid to the negative source of supply.

4. A system for regulating voltage comprising a source of direct current potential supply having an intermediate point grounded, a first tube, a second tube, and an output tube each having at least an anode, cathode and grid, an output circuit connected from the output tube cathode to ground, a voltage divider connected from the output cathode to the negative source of supply, a connection from the voltage divider to the first tube grid, an anode resistor for the first anode, a connection from the first anode to the second grid, a, regenerative connection for the first tube including a cathode resistor for the first tube connected to ground and a cathode resistor for the second tube connected to the cathode of the first tube, and negative bias means interposed between the second tube and the output tube including a glow discharge voltage regulator tube having an anode and a cathode connected respectively to the second tube cathode and the grid of the output tube and a high resistance connecting the cathode of the regulator tube to the negative potential source.

5. A system for regulating voltage comprising, a source of direct current potential supply having an intermediate point grounded, a load resistance one end of which is grounded and a vacuum tube in series with the potential source and load resistance for controlling the current, vacuum tube means responsive to the load voltage for controlling the load current tube, and vacuum tube means responsive to the supply voltage for controlling first mentioned means, said first mentioned means including a triode having an anode and cathode resistor, a cathode follower tube, a glow discharge voltage regulator tube and a voltage divider connected from the positive load terminal to the negative source of supply, a connection from the voltage divider to the grid of the triode, a connection from the plate of the triode to the grid of the cathode follower tube, a re 5 generative connection for the triode including a cathode resistor for the cathode follower tube connected to the cathode of the triode, a. connection from the cathode of the cathode follower tube to the anode of the voltage regulator tube, a connection from the cathode of the voltage regulator tube to the grid of the load current tube, and a high resistance connected from the oathode of the voltage regulator tube to the negative source of supply, said supply voltage responsive means including a second voltage divider bridged across the source of supply voltage and a second triode having its cathode connected to ground, its anode connected to the anode of said first triode and its grid connected to said second voltage 15 2,434,724

divider.

CHARLES F. HOBBS. NORMAN B. SAUNDERS.

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